Recent advances in the size and performance of micro-electromechanical systems (MEMS)-based inertial instruments enable the development of a prosthesis to provide information about head motion to vestibulopathic patients. One class of candidate users is individuals who have lost some or all vestibular function and would benefit from an artificial vestibular system to augment natural visual and nonvestibular proprioceptor balance cues. A second class of users is patients with vestibular lesions who experience asymmetric firing between bilateral vestibular receptor organs. Such patients may be able to take advantage of artificial vestibular cueing, particularly since head motion is likely to exacerbate their symptoms. A third class of users is patients with balance deficits due to vestibular disorders or stroke who are undergoing vestibular rehabilitation therapy. To evaluate the utility of the Vestibular Improvement Prosthesis (VIP) whose development is proposed herein, patients with bilateral vestibular deficits will perform computerized dynamic posturography and dynamic subjective visual vertical tests. The specific hypothesis tested is that these patients will perform posturographic and eccentric rotational testing significantly better using the proposed VIP. Based on these experiments and a "usability" analysis, a product prototype will be constructed and tested in Phase II.